The present invention relates to a beam in a vehicle comprising a box-shaped member made of bent sheet metal and having a greater length than both width and height. The box-shaped member also has a portion oriented in the longitudinal direction of the vehicle and that has, at a distance from one end, an area made so that the stiffness of the beam in the longitudinal direction is suddenly reduced after the beam has been deformed a pre-determined distance beginning from said end.
Box beams appear in a number of different applications in automobiles. As an example, such beams are utilized as front lateral members in passenger car chassis and are thus components, the design of which crucially affects the collision safety of the automobile. One method of achieving high collision safety through crash control is to force, as much as possible, the elements in the structure to be deformed in the most energy-absorbing manner, which is progressive crushing or fold formation. Less energy-absorbing modes, such as rigid body rotation or bending, should thus be avoided.
From the point of view of crash safety, the ideal situation would be to allow the volume represented by the forward portion of the car to consist of a large number of cells, each having a large energy-absorbing capacity regardless of from which direction the car is struck. Such solutions, however, have not been able to be employed in mass production for a number of reasons.
Test vehicles have been manufactured in which foam plastic-filled box beams have been used to achieve controlled deformation. Such vehicles have, however, never been produced in large volumes. The reasons are many, but the most important are the high costs connected with complicated manufacturing processes and the effect on the environment of harmful chemicals in the foam used.
Normally, the beam member system in a vehicle is regarded as a passive security system where it is primarily the geometric shape of the box beams which, through their energy-absorbing capacity, determine the collision safety. It is, however, known to arrange in a vehicle an xe2x80x9cactivexe2x80x9d beam system; that is, a system where a collision triggers an activity which makes the beam system act in a certain manner beyond its normal mechanical limitations. Such an active beam system is shown, for example, in U.S. Pat. No. 4,050,537. In the ""537 patent, an explosive charge is used in the event of a collision to change a cross section of a box beam in such a manner that the beam""s stiffness, and thus its energy-absorbing capacity, increases.
In view of the above described deficiencies associated with known box beam designs for vehicles, the present invention has been developed. These enhancements and benefits are described in greater detail hereinbelow with respect to several alternative embodiments of the present invention.
The present invention in its several disclosed embodiments alleviates the drawbacks described above with respect to conventionally designed vehicular box beams and incorporates several additionally beneficial features.
The purpose of the present invention is, in general, to achieve a simple and inexpensive active beam arrangement of the type described by way of introduction which avoids less energy-absorbing modes such as rigid rotation and bending.
This is achieved, according to the invention, by virtue of the fact that the box-shaped member is stiffened in relevant areas by means of stiffeners fixed to the box profile. The stiffeners are arranged to split off when the beam has been deformed a predetermined distance. The stiffeners can be simple plates which are glued to the beam with an adhesive which provides a hard and brittle glue joint; for example, an epoxy glue. If the areas under the plates are, for example, stamped, folded, perforated or of smaller thickness than the rest of the beam plate, a substantial reduction in the stiffness of the beam can be obtained in these areas when the glue joint breaks and the plates are shed.
A beam, arranged according to the invention, is thus considered an active beam. By studying the deformation of a passive beam after a collision, it is possible to determine where the transition occurred between upsetting or fold formation, and buckling of the entire beam. By actively softening the beam in this failure area, buckling can be avoided during deformation. As a result of the softening, the area in which fold formation occurs is extended also across the softened area up to the area behind it, which can be stiffer.
The beneficial effects described above apply generally to the exemplary systems and methods for improving box beam performance. The specifics through which these benefits are enabled will be described in detail hereinbelow.